Rotate the ball, torch the obliques.
Turn from your ribcage, not just your arms, and keep your chest tall.
Leaning back to 45 degrees puts your abs under a constant isometric hold, then every twist makes the obliques rotate your torso against the ball's inertia. Because you tap the ball hip to hip, each side takes its turn driving the rotation while the other decelerates it, which is exactly how the obliques work in sport. It earns its spot as rotational core work in a training week that is otherwise all crunching and bracing.
Keeping heels light on the ground is the standard version and lets you focus on rotating well. Lifting your feet off the floor is a progression that adds a balance demand, earn it first.
Light enough that your ribcage does the turning, not your arms swinging the ball around. If your chest collapses or you start whipping the ball with your hands, drop the weight.
A tap beside the hip is a good target for full range, but the quality of the rotation matters more than the touch. Twist until your shoulders face sideways, then come back through the middle under control.
